inflames instantly with great brilliancy, as do also the lighter
varieties of wood charcoal. A curious phenomenon is noticed with wood
charcoal; it appears at first to absorb and condense the fluorine,
then quite suddenly it bursts into flame with bright scintillations.
The denser varieties of charcoal require warming to 50° or 60° before
they inflame, but it once the combustion is started at any point it
rapidly propagates itself throughout the entire piece. Graphite must
be heated to just below dull redness in order to effect combination;
while the diamond has not yet been attacked by fluorine, even at the
temperature of the Bunsen flame. A mixture of gaseous fluorides of
carbon are produced whenever carbon of any variety is acted upon by
fluorine, the predominating constituent being the tetrafluoride,
CF_{4}.

_Boron._--The amorphous variety of boron inflames instantly in
fluorine, with projection of brilliant sparks and liberation of dense
fumes of boron trifluoride, BF_{3}. The adamantine modification
behaves similarly if powdered. When the experiment is performed in the
fluorspar tube, the gaseous fluoride may be collected over mercury.
The gas fumes strongly in the air, and is instantly decomposed by
water.

_Silicon._--The reaction between fluorine and silicon is one of the
most beautiful of all these extraordinary manifestations of chemical
activity. The cold crystals become immediately white-hot, and the
silicon burns with a very hot flame, scattering showers of star-like,
white-hot particles in all directions. If the action is stopped before
all the silicon is consumed, the residue is found to be fused. As
crystalline silicon only melts at a temperature superior to 1,200°,
the heat evolved must be very great. If the reaction is performed in